Auditory system

Question 1

what is the anatomy of the auditory system?

Answer 1

• Divided into 3 sections
  
  • Outer, middle and inner ear
• Each part has specific function
• Organ embedded in petrous portion of temporal bone (hardest bone in body)

Question 2

what is the function of the outer ear?

Answer 2

capture sound and focus it on the tympanic membrane

amplify some frequencies by resonance in the canal

protect the ear from external threats

Question 3

what is the function of the middle ear?

Answer 3

• Main function is amplification by:
  
  • Focusing vibration from large surface area (tympanic membrane) to smaller surface area (oval window)
    
    • Change surface area means pressure in increased
  • Using leverage from incusstapes joint to increase force on oval window

Question 4

what is the function of the inner ear?

Answer 4

• Hearing part inner ear is cochlea
• Function = transduce vibration into nervous impulses
• While doing so produces a frequency (pitch) and intensity (loudness) analysis of sound

Question 5

what does the cochlea contain?

Answer 5

3 compartments

• Scala vestibuli
• Scala tympani
• Scala media

Question 6

what are the scale vestibuli and tympani?

Answer 6

bone structures

contain perilymph (high in sodium)

Question 7

what is the structure of the scala media?

Answer 7

membranous structure

contains endolymph (high potassium)

hearing organ of Corti location

Question 8

what is the structure where the organ of corti lies?

Answer 8

basilar membrane

Question 9

how is the basilar membrane arranged?

Answer 9

tonotopically

sensitive to different frequencies at different points along length

Question 10

what is the hearing organ?

Answer 10

organ of corti

Question 11

what does the organ of corti contain?

Answer 11

• Contains hair cells: inner (IHC) and outer (OHC)
• IHC arranged on one column and OCH on three
• tectorial membrane above hair cells
  
  • allow hair deflection, which will depolarise the cell
  • only OHC in constant contact with membrane
    
    • assists contacts with the IHC

Question 12

what are the function of inner hair cells?

Answer 12

carry 95% afferent information of auditory nerve

function= transduction of sound into nerve impulses

Question 13

what are the function of outer hair cells?

Answer 13

carry 95% efferent information of auditory nerve

function= modulation of sensitivity of response

Question 14

what is the difference between inner and outer hair cells?

Answer 14

IHC arranged in one column, OHC on 3

OHC in constant contact with tectorial membrane

Question 15

what are sterocilia?

Answer 15

hairs of hair cells

responsible for transduction

Question 16

how does deflection of stereocilia work?

Answer 16

open K+ channels= deflection of sterocilia towards longest cilium

• ionic interchange depolarises the cell= NT liberated

Question 17

what are the effects of depolarisation in hair cells?

Answer 17

K+ channel opening

Question 18

what happens to deflection of stereocilia with higher amplitude of sound?

Answer 18

higher amplitude of sound= greater deflection of stereocilia & K+ channel opening

Question 19

what happens to stereocilia on hyperpolarisation?

Answer 19

closes K+ channels so noises arent as loud

Question 20

what is the pathway from the cochlear to cerebral hemisphere?

Answer 20

• spiral ganglions from each cochlear project via auditory vestibular nerve (VIII) to ipsilateral cochlear nuclei
• auditory information crosses at superior olive level
• after this point all connections are bilateral

Question 21

how is hearing organised centrally?

Answer 21

tonotopically organised

Question 22

what is frequence / pitch?

Answer 22

(Hz)= cycles per second, perceived tone

Question 23

what is amplitude/loudness?

Answer 23

(db)

sound pressure, subjective attribute correlated with physical strength

Question 24

what is the human range of hearing?

Answer 24

• freq = 20-20,000 Hz
• loudness= 0dB- 120 dB sound pressure level (SPL)

Question 25

what is hearing acuity affected by?

Answer 25

decreases with age, particularly higher frequencies

Question 26

what are the types of hearing assessments?

Answer 26

tuning forks audiometry central processing assessment tympanometry otoacoustic emission auditory evoked potentials

Question 27

what do tuning forks do?

Answer 27

* establish probable presence or absence of hearing loss with significant conductive component * provide early and general information when audiometry is not available or possible * webber and rinne test * vibrate fork and see if hearing loss asymmetric or symmetric * not very specific tests

Question 28

what is audiometry?

Answer 28

* science of measuring hearing acuity for variations in sound intensity and frequency * produce an audiogram where hearing thresholds plotted

Question 29

what is central processing assessment?

Answer 29

* assessment hearing abilities via verbal and non verbal tests * e.g sound localisation, speech in noise, filtered speech

Question 30

what is tympanometry?

Answer 30

* test middle ear and mobility of eardrum and conduction bones by creating vibrations of air pressure in ear canal

Question 31

what is otoacoustic emission?

Answer 31

* low intestity sounds produced by normal cochlea * produced specifically by outer hair cells as expand and contract * part of newborn hearing screening and hearing loss monitoring * require no cooperation of subject

Question 32

what are the types of auditory evoked potentials?

Answer 32

* electrocochleography * electrical activity from cochlea and 8^th nerve- evoked by clocks or tone burst * auditory brainstem response (ABR) * electrical activity from 8^th nerve and brainstem nuclei and tracts- evoked by clicks * late responses * electrical activity from primary auditory and association cortex- evoked by tone burst and oddball paradigm

Question 33

what are auditory brain stem responses and how are they used?

Answer 33

* electrical responses from auditory pathway * ABR more commonly used in clinics * Does not require attention from patients * Alterations in latency of waves can point the location of deficit

Question 34

when might cortical potential be affected?

Answer 34

neurological condition or processing problems

Question 35

what are the types of hearing loss?

Answer 35

conductive hearing loss sensorineural hearing loss mixed hearing loss

Question 36

what is conductive hearing loss due to?

Answer 36

problem located in outer or middle ear

Question 37

what is sensorineural hearing loss due to?

Answer 37

problem located in the inner ear or auditory nerve

Question 38

what is mixed hearing loss due to?

Answer 38

conduction and transduction affected problem affects more than one part of ear

Question 39

what are the degrees of hearing loss?

Answer 39

depends on where hearing thresholds are located can be mild, moderate, severe or profound

Question 40

what are the causes of conductive hearing loss?

Answer 40

Question 41

what are the causes of sensorineural hearing loss?

Answer 41

Question 42

what are the treatments for hearing loss?

Answer 42

1. Underlying cause 2. Hearing aids/ cochlear implants/ brainstem implants

Question 43

what do hearing aids do?

Answer 43

* Amplify sound, does not replicate any structure

Question 44

what do cochlear implants do?

Answer 44

* Replaces function of hair cells by receiving sound, analysing and transforming into electrical signals * Send electrical impulse directly to auditory nerve * Required functional auditory nerve to function

Question 45

what do brainstem implants do for hearing loss?

Answer 45

Electrical signal sent to electrode in brainstem when auditory nerve affected- risky! Only bilateral nerve damage